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Date: Thu, 29 Nov 2018 12:41:25 +0100
From: Cornelia Huck <cohuck@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 1/6] s390x/vfio: ap: Finding the AP
 bridge
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To: Pierre Morel <pmorel@linux.ibm.com>
Cc: borntraeger@de.ibm.com, agraf@suse.de, rth@twiddle.net, david@redhat.com, qemu-s390x@nongnu.org, qemu-devel@nongnu.org, peter.maydell@linaro.org, pbonzini@redhat.com, mst@redhat.com, eric.auger@redhat.com, akrowiak@linux.ibm.com, pasic@linux.ibm.com

On Thu, 22 Nov 2018 17:35:50 +0100
Pierre Morel <pmorel@linux.ibm.com> wrote:

> In the case we will enter QEMU through interception of instructions,
> we will need to retrieve the AP devices.
> The base device is the AP bridge.
> 
> Let us implement a way to retrieve the AP Bridge from qtree.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  hw/s390x/ap-bridge.c         | 12 ++++++++++++
>  include/hw/s390x/ap-bridge.h |  1 +
>  2 files changed, 13 insertions(+)
> 
> diff --git a/hw/s390x/ap-bridge.c b/hw/s390x/ap-bridge.c
> index 3795d30..831ad5d 100644
> --- a/hw/s390x/ap-bridge.c
> +++ b/hw/s390x/ap-bridge.c
> @@ -14,6 +14,18 @@
>  #include "hw/s390x/ap-bridge.h"
>  #include "cpu.h"
>  
> +DeviceState *s390_get_ap_bridge(void)
> +{
> +    static DeviceState *apb;
> +
> +    if (!apb) {
> +        apb = DEVICE(object_resolve_path(TYPE_AP_BRIDGE, NULL));
> +        assert(apb != NULL);

As you won't have an ap bridge if the ap feature is not provided,
better do a quick exit if the feature bit is not set? I'd naively
assume that this function can return NULL as well.

> +    }
> +
> +    return apb;
> +}
> +
>  static char *ap_bus_get_dev_path(DeviceState *dev)
>  {
>      /* at most one */